1. Field of the Invention
The present invention relates generally to an apparatus and method for controlling noise in a mobile communication terminal, and more particularly to an apparatus and method for controlling a volume of comfort noise received in a silence period during a call connection state of a mobile communication terminal.
2. Description of the Related Art
Generally, while a user of a calling mobile communication terminal, namely, a calling user, is in a call connection state with a user of a called mobile communication terminal, namely, a called user, there may be a silent period during which the calling user does not talk to the called user. Such a period is typically referred to as a silence period. In this silence period, no voice signal containing the calling user's voice, but a noise signal containing only ambient noise, i.e., noise around the calling mobile communication terminal, is transmitted to a vocoder of the called mobile communication terminal. The vocoder may be generally of an EVRC (Enhanced Variable Rate Speech Codec) type or a QCELP (Qualcomm Code Excited Linear Predictive) type. The EVRC-type vocoder is employed in a CDMA (Code Division Multiple Access)-type mobile telephone service and codes voice information at variable rates based on the amount thereof. In a similar way to the EVRC-type vocoder, the QCELP-type vocoder codes voice information at variable rates based on the amount thereof. That is, in a speech period where a speaking user talks a lot, voice information is coded at a high rate because the amount of voice information is large. On the other hand, in the silence period where the speaking user does not talk, voice information is coded at a low rate since the amount of voice information is close to zero.
As described above, in the silence period, a conventional mobile communication terminal transmits data at a rate different from that in the speech period in the QCELP or EVRC manner. That is, in the silence period, the vocoder of the calling mobile communication terminal compresses data containing only ambient noise so that the amount thereof becomes ⅛ that of information in the speech period, and transmits the resulting ⅛-rate data to the called mobile communication terminal. The vocoder of the called mobile communication terminal receives the ⅛-rate data and reproduces only noise of a certain level in the received data, enabling the called user to hear the noise. The noise reproduced in the silence period is typically referred to as comfort noise, which is intrinsic to a vocoder, such as the EVRC-type or QCELP-type vocoder. The comfort noise provides the called user with a more comfortable conversation environment. Without the comfort noise, the called user may not hear any sound from the calling user in the silence period, therefore the called user may think that the current call has been disconnected or feel as if he/she is in a sound-free room where no ambient noise exists. The comfort noise is not noise typically produced by hardware (H/W) circuitry, but rather intentionally provided. In this regard, the comfort noise is different from any other noise, such as extraneous noise produced in the speech period, which should be completely removed. Conventionally, because the receiving volume of a mobile communication terminal is set to a low level, the comfort noise is reproduced at such a low volume that it is unable to be recognized as typical noise by a user. However, as the standard level of the receiving volume has increased significantly according to users' demands and market trends, recently, the receiving volume has been set to a higher level. Accordingly, the volume of the comfort noise in the silence period has been raised with the receiving volume of voice data in the speech period in the call connection state.
FIG. 1 illustrates a conventional apparatus for receiving and outputting a voice signal in a mobile communication terminal. As illustrated in FIG. 1, a radio frequency (RF) unit 102 is provided to receive voice data, which is then processed via a vocoder 104, an internal codec 106, and an external codec 110 such that it is output at a receiving volume set by a user. It can be seen from this construction that the receiving volume of the voice data is amplified to a high level set to meet the current demand for the high receiving volume standard level. However, the comfort noise, generated in the silence period in the call connection state, is over-amplified, thereby providing its intrinsic function, but also causing white noise that results in the user's dissatisfaction. In this regard, there is an increased need to prevent the over-amplification of the comfort noise in the silence period after establishment of a call in the mobile communication terminal.
As described above, in the past, because the standard level of the receiving volume of a mobile communication terminal had been set to a low level, the comfort noise received in the silence period was reproduced at such a low volume as not to be recognized as typical noise by a user. However, recently, because the receiving volume has been significantly raised in compliance with users' demands and market trends, not only has the receiving volume been raised, but also the output volume of the comfort noise in the silence period has been increased to such a level as to cause the users' dissatisfaction. For this reason, the comfort noise has caused white noise in addition to the provision of its intrinsic function. Therefore, a need exists to reduce the level of white noise by controlling the volume of the comfort noise received in the silence period in the call connection state.